Anyone can sell Mobi format books (eg Baen do). What you can't do, though, is licence Amazon's DRM. If you want Amazon DRM, you have to sell through Amazon.

Yep if you needed a license to provide mobi format books to people I imagine MR wouldn't be here either. While MR doesn't charge for its mobi format ebooks if you needed a license to provide them to others I wager it would be an expensive proposition to get such a license.